As is known in the art, Network Attached Storage (NAS) is a data storage mechanism that allows a host device to access storage devices using an Internet Protocol (IP) network. NAS devices are generally file servers that are referenced using IP addresses and are coupled to storage media, such as a RAID array or the like. The NAS therefore serves as a gateway between the storage media and the network. One example of the use of NAS can be found in the Celerra NS600 Network Server, from EMC Corporation of Hopkinton Mass. which includes a front end NAS enclosure and a back end Clariion storage enclosure.
One advantage of the NAS structure is that it enables data storage, data security and data management to be centralized in an environment with many servers running different operating systems. In addition, the use of a NAS-based system such as the Celerra system from EMC is a simple and straightforward way for a host to expand its storage capacity through the use of existing IP host functionality.
Although NAS-based systems are useful, to provide consistent, high performance client support, businesses typically rely on high availability systems. In the prior art, high availability characteristics have been added to a NAS system by duplicating the data mover front end enclosure. For example, a block diagram of an exemplary NAS architecture 10 with some high availability characteristics is shown in FIG. 1. The NAS 10 includes a pair of data mover enclosures 16a and 16b which control the movement of data to and from the attached storage device (not shown). In the example of FIG. 1, each data mover enclosure is shown to include two data movers, which together provide some level of high availability to the overall NAS by enabling continued data mover operation in the event of a single point of failure. A control station 12 is used to monitor the operating status of the data movers. A switch is disposed between the control station 12 and the data mover enclosures 16a and 16b for forwarding control information between the control station and the data movers. Data that is read from or written to the data storage device is forwarded to and from the data movers via an External Local Area Network (LAN), not shown.
Although the NAS architecture 10 provides some level of high availability, because the architecture uses only a single switch and control station, a single point of failure can cause the control system to fail, and therefore the system may not have the required rate of reliability.
FIG. 2 shows an exemplary high availability NAS architecture which overcomes single point of failure issues. The high-availability NAS 20 includes two control stations 12 and 22 coupled via two switches to the two data mover enclosures 16a and 16b. In the event of a single point of failure at any of the components, the remaining component can cover for the failed component while it is repaired.
The solution of FIG. 2 is thus capable of providing high availability support in a NAS environment. One particular problem with such an arrangement, however, involves the physical connections between the individual components of the system. Each line in FIG. 2 that connects one component to another component represents a connection between the components, such as an Ethernet cable. As the components are doubled, the number of cables is linearly increased to ensure that all necessary connections for supporting the high availability system can be maintained. For example, the four cables that were previously used to couple the data movers to the switch are increased to eight cables. The sheer number of cables that would need to fit within the enclosure makes such an arrangement undesirable, and makes any further scaling of the design prohibitive.
Referring briefly to FIG. 3, a diagram of the exemplary NAS enclosure system of FIG. 2 is shown illustrating the clutter of cables within the enclosure, including Ethernet cables from the switches 14 and 24 to the components, and control cables (for example RS485 control cables) from the control stations 12 and 22 to the components.